Honda: transmission pops out of 4th gear, transmission shifts, 1987 honda accord

Question
1987 Honda Accord automatic 4 speed. Transmission shifts fine into all gears and then at cruising speed, about 40-45 mph, the transmission disengages from 4th gear. I can then downshift into 3rd and it runs fine in 3rd but will not re-engage into 4th if I manualy try to shift it. Is there a sensor or something that I can replace to fix this problem or is it an overhual issue or what? The car has 185,400 miles on  it. Thanks, Chris

Answer
Do you do a lot of interstate driving.  What sometimes happens is a certain gear will become overheated.  It is caused by the gear being under constant heavy load and not spinning fast enough for the oil to cool it sufficiently (constant speed).  Be glad it's your overdrive gear and not second.

Seems like it's time for a major service...but it is definitely worth a look at the possibility of an overdrive issue.  

Hope I helped,
B